Method and apparatus for degassing liquids in a vacuum



Jan. 7, 1964 w. ARMBRUSTER 3,116,999

METHOD AND APPARATUS FOR DEGASSING LIQUIDS IN A VACUUM Filed Feb. 20, 1961 INV ENT OR WERNER ARAJBRUS TE R Bur/M W gfls United States Patent O 3,116,999 METHD AND APPARTHJS FR DEGASSNG LlQUi-DS EN A. VACUUM Werner Arm raster, Hanan (Main), Germany, assigner of one-half to W. C. GmbH., and of one-half to Ruhr-stahl Aktiengesellschaft, Hanau (Main) and Hattingen (Ruhr), Germany, respectively, both corporations of Germany Filed Feb. Ztl, 196i, den No. 90,474 Claims priority, application Germany Mar. l2, 1960 '7 Claims. (Cl. 75-49) The present invention relates to an apparatus for degassing liquids, and especially liquids of a low density, by the circulatory degassing .i ethod by means of a vacuiun in which the respective liquids rise to a barometric height of several meters or more.

lt is an object of the invention to provide an apparatus of the above-mentioned type which is adapted to reduce the actual height of rise of the liquid to be degassed coniderably below the barometric height so that the entire degassing apparatus may be made of a considerably smaller size.

A further object of the invention is to provide such an apparatus which is also adapted to be used for degassing liquid materials of a high density, for example, molten steel, and for also reducing the height of rise of such liquids to a considerably lower level than the barometric height.

Thus, the new apparatus is designed to reduce, for example, the height of rise of molten steel in the evacuated degassing vessel from the normal full barometric height of apprordmately 1.40 m. to a height of only a few decimeters, so that the Sile of the entire degassing apparatus may be reduced accordingly. This advantage attained by the present invention is even more apparent if liquids of a low density are to be degassed, for example, plastisols, or organic liquids such as mineral oils with a density of approximately 0.8 and a barometric height of approximately l2 m. rl`he invention is, however, also applicable to metals such as aluminum with a density of 2.7 and a barometric ceiling of approximately 3.7 m.

The circulatory degassing method has been very frequently applied in recent times for the purpose of degassing steel by means of a vacuum. According to this method, a degassing vessel which is adapted to be evacuated is provided with a pair of substantially vertical, downwardly extending pipes, the ends of which are immersed from above into the molten steel which is to be degassed. A suitable conveying gas is then conducted into one of the pipes and, because of its considerably lower density, this gas will rise quickly within this pipe and thereby take along the liquid metal into the evacuated degassing vessel. Due to the vacuum in the degassing chamber of this vessel, the gases contained in the molten metal as well as the conveying gas are then extracted from the metal, and the degassed metal then ilows through the second pipe back to its container in which it becomes mixed with the remainder of molten metal. The container of the metal generally consists of a casting ladle, the upper end of which is completely open so that the molten metal therein is under atmospheric pressure and covered merely by a layer of slag.

Since according to this method the liquid to be degassed, for example, the molten metal, is maintained in its container under a normal atmospheric pressure, it will rise in both pipes to a level in accordance with the differential pressure relative to the vacuum which is maintained in the degassing vessel. At a sufhcient vacuum, the liquid will then rise in the pipes to the barometric height. Since the specific gravity of iron and also of steel alloys amounts approximately to 7.8, the barometric height thereof amounts to approximately 1.4 m. Even though such an apparatus has still a relatively small size, it may in certain cases be still too large so that a reduction in size may be desirable or necessary.

lf the circulating method as described is to be applied for the purpose of degassing other liquids which have a considerably lower density, the barometric height would be considerably higher and the required apparatus would therefore be very high. Also if liquids are to be degassed at a higher temperature or if they have a higher melting temperature, for example, aluminum, they would cool off excessively within the necessary long pipes leading from the liquid container to the degassing vessel.

These disadvantages will be overcome by applying the method according to the present invention. It constitutes a valuable improvement over the conventional circulatory degassing method, and this improvement is attained by closing the container for the liquid which is to be degassed by means of a cover and by evacuating it by means of a vacuum pump through a pipe leading into the container. The liquid to be degassed is therefore no longer maintained under a normal atmospheric pressure, but under a vacuum of a size which is dependent upon the size of the preliminary pump. A second vacuum pump is connected to the degassing vessel and produces therein a reduced pressure which is still lower than the vacuum which is produced by the first pump in the container above the surface of the liquid. This second pump for producing the necessary differential pressure is preferably a Roots-type pump. The height to which the liquid has to rise is therefore now dependent upon the differential pressure which is produced by the Roots-type pump between the reduced pressures in the liquid container and in the degassing vessel. In order to permit this height to be varied, the Roots-type pump may be provided either with a by-pass which contains a control valve which permits the `Aifferential pressure to be varied or the suction outlet of the liquid container may 'ce connected to a control valve which likewise permits the height of rise to be varied. It is also possible to use both of these control means in combination with each other.

These objects, features, and advantages of the present invention will become more clearly apparent from the following detailed description of a preferred embodiment thereof as illustrated in the accompanying drawing.

The apparatus according 4to the invention consists of a container 2 which is closed by a cover 3 and holds the liquid l which is to be degassed. The liquid may be filled into the container through an inlet pipe i and may be discharged therefrom Ithrough an outlet pipe o. A pair `oi pipes S and extend upwardly through the cover 3 and their free lower ends are immerse-d into the liquid l, While the upper ends are connected to the bottom of the devassing vessel lil. Pipe 8 serves as an inlet pipe ffor conducting the liquid linto de-gassing vessel lil', and for this purpose a suitable conveying gas of a considerably lower density than the liquid to be degassed is conducted into pipe thsough a pipe ll so that this gas, while rising in pipe S, will take along the liquid into the degassing vessel lil in the direction as shown by arrow l2. After passthrough vessel lil, the liquid Hows out thro-ugh pipe 9 and downwardly in the direction of arrow i3 into the main body o-f liquid ll in container 2.

rlhe chamber in container 2 above the surface 'of liquid l is evacuated through pipe le" by means of a preliminary vacuurn pump i6, while the degassing chamber in vessel lil is evacuated by a Roots-type pump 19 through pipe 17 and through a vapor and dust separator i8. Thus, by means of the Roots-type pump 19, a differential pressure is established through the connecting pipe l5 between the degassing chamber l@ and the chamber in container 2 above the surface of liquid l.

The height of rise lol the liquid which lis dependent upon the size of Ithis differential pressure may in some cases be very great. in order to reduce this height, a bypass 2S with a control valve 2l is provided by means of which the diiierential pressure may be regulated. li control valve 21 lis fully opened, lthe result of the operation of pump i9 is practically no more than that the gases will be sucked up through by-pass Ztl. lf val-ve 2l is, however, almost efntirely closed, the diterential pressure which is produced by the Roots-type pump l@ between the chamber in container 2 above the surface of liquid l and the inside of degassing vessel it? will be only slightly reduced.

Instead of regulating the differential pressure by means of luy-pass Ztl and control -valve 2l, .it is also possible to do this by means of a control valve 22 which is inserted into pipe l5. Especially it is possible to increase the differential pressure considerably by substantially closing valve 222 lwhich will promote the liberation of gases from the liquid in container 2. in order :to vary the rise of the liquid, so as either to increase or decrease it, it is advisable to provide both valves Zit and 22 and by-pass 2t?.

Att the inside of degassing vessel lil', inclined guide plates 2.5' or the like are preferably mounted along which the liquid to be degassed may flow downwardly in the form of a thin layer and will therefore be exposed for a greater length of time to the vacuum within vessel iti. In some cases it may also be advisable to provide the upper end of inlet pipe S with a nozzle 2o so that the liquid to be delgassed, for example, mineral oil, will be ejected into degassing vessel lil in the form ot a fountainl-ike spray. ln order to prevent larger drops of liquid from entering into suction pipes 15 and i7, suitable battles 3% or the like may also oe provided in container 2 and vessel l@ in ttnont `of the openings into these pipes.

For controlling the apparatus, vacuum gauges 35 and 36 are provided for measuring the pressure in container 2 above the surface of liquid Il and in the degassing vessel lil. Furthermore, in order to measure the differential pressure directly and for determining fthe exact height of rise of the liquid, .it is also advisable to provide a differential pressure :gauge which measures the dit'erence in pressure between the two chambers.

Between line il and, for example, the connection between the differential pressure gauge and container 2 it is also possible to provide a pressure relief valve. Such a valve may also be used in place of or in addition to the control valve 2l.

By provi-ding a preliminary vacuum in container 2, the method according to the invention attains a preliminary degasii'lcation of the liquid before it passes through the degassing vessel Tril, and this preliminary degasiiication will be rendered still more -eicient by the continuous circulation of the liquid through lthe dcgassing vessel lo. The high vacuum in degassing vessel i@ serves so-to-speak as a second degassing stage in which the remainder oi' the gases contained in the liquid will be extracted therefrom.

Although my invention has been illustrated and described with reference to the preferred embodiments thereof, I wish to have it understood that it is in no way limited to the details of such embodiments, but is capable of numero-us modifications within the scope of the appended claims.

One of these modiiications may be mentioned especially. It consists in the use of a special and separate container for 4the liquid i to be rdegassed, so that in this case the container 2. is no longer used `as a container for the liquid, but as a `vacuum chamber 'in which the Said special and separate container is to be placed. Such a container can be inserted into the evacuated chamber 2 or removed from it when the upper cover together with the degassing vessel lli? and the pipes S and 9 have been raised to a suiicient height. The special and separate container may be a ladle containing molten metal. As this l. In a continuous recycling method for vacuum degasication of molten metals and having as the steps of such method continuously passing molten metal from a molten metal Zone upward in a contined stream and with the aid of a lifting gas into a vacuum degasication Zone and continuously discharging treated molten metal from said vacuum degasication zone downwardly into said container zone into said molten metal zone below the level of the molten metal therein, and at a point external to and spaced apart from the point at which the molten metal is again continuously moved upward, the improvement which comprises in combination with said steps substantially maintaining a vacuum above the molten metal in said molten metal zone, and substantially maintaining a pressure differential between the vacuum in said degasication Zone and the vacuum in said molten metal zone with the vacuum in said rst mentioned Zone being greater than in said last mentioned zone to thereby assure a barometric height for the discharging ot the confined stream ot molten metal, which is less than the normal barometric height thereof.

2. In a continuous recycling device for the vacuum degasification of molten metal and having as elements vacuum degassing chamber means, a lower positioned container tor holding molten metal, riser conduit means for conveying molten metal from said container to said chamber means, discharge conduit means for discharging molten metal from said chamber into said container, means for forcing gas bubbles into and through said riser conduit means, said riser and said discharge conduit means being with their immersion ends arranged in nonconcentric separate and spaced relation, the improvement which comprises, in combination with said elements, such container in substantially closed form, means for evacuating the upper portion of said container and means for maintaining a diierential vacuum between said degassing chamber means and said container with a greater evacuation for said chamber means.

3. An apparatus as defined in claim 2, in which said evacuating means comprise a rst and second suction pump, a pipe connecting said container to the suction side of the rst pump, and a pipe connecting said degassing chamber means to the suction side of the second pump, means for connecting the pressure side of said second pump to the pipe connecting said container to the suction side of said rst pump.

4. An apparatus as delined in claim 3, further comprising a control valve inserted into said pipe connecting said container to said first pump for varying the differential pressure produced by said pumps between said container and said degassing chamber means.

5. An apparatus as dened in claim 2, in which said evacuating means comprise a rst and second suction pump, a pipe connecting said chamber to the suction side of the i'irst pump, and a pipe connecting said degassing, chamber means to the suction side of the second pump, a pipe connecting the suction sides of said two pumps to each other, and a control valve inserted n said last pipe. for varying the differential pressure produced by said pumps between said container and said degassing chamber means.

6. An apparatus as deined in claim 2, further ctn-ripris-l ing guiding means Within said degassing chamber means for receiving the liquid injected into said chamber means through one of said pipes and for guiding said liquid so as to ilow in a thin layer in a downward direction along said guiding means.

7. An apparatus as delined in claim 2, further comprising nozzlelike means in said degassing chamber means on the end of said pipe into which said gas is inserted for directing said liquid in a fountainlike spray into said chamber means.

References Cited in the file of this patent UNITED STATES PATENTS Brennan Apr. 21, 1959 l 6 2,893,860 Lorenz July 7, 1959 2,997,756 Strom Aug. 29, 1961 FOREIGN PATENTS 683,996 France Mar. 10, 1930 OTHER REFERENCES Vacuum Metallurgy by Rointan F. Bunshah, published by Reinhold Publishing Corp., New York, New York, 1958, pp. 249-254 and 280-282. 

1. IN A CONTINUOUS RECYCLING METHOD FOR VACUUM DEGASIFICATION OF MOLTEN METALS AND HAVING AS THE STEPS OF SUCH METHOD CONTINUOUSLY PASSING MOLTEN METAL FROM A MOLTEN METAL ZONE UPWARD IN A CONFINED STREAM AND WITH THE AID OF A LIFTING GAS INTO A VACUUM DEGASIFICATION ZONE AND CONTINUOUSLY DISCHARGING TREATED MOLTEN METAL FROM SAID VACUUM DEGASIFICATION ZONE DOWNWARDLY INTO SAID CONTAINER ZONE INTO MOLTEN METAL ZONE BELOW THE LEVEL OF THE MOLTEN METAL THEREIN, AND AT A POINT EXTERNAL TO AND SPACED APART FROM THE POINT AT WHICH THE MOLTEN METAL IS AGAIN CONTINUOUSLY MOVED UPWARD, THE IMPROVEMENT WHICH COMPRISES IN COMBINATION WITH SAID STEPS SUBSTANTIALLY MAINTAINING A VACUUM ABOVE THE MOLTEN METAL IN SAID MOLTEN METAL ZONE, AND SUBSTANTIALLY MAINTAINING A PRESSURE DIFFERENTIAL BETWEEN THE VACUUM IN SAID DEGASIFICATION ZONE AND THE VACUUM IN SAID MOLTEN METAL ZONE WITH THE VACUUM IN SAID FIRST MENTIONED ZONE BEING GREATER THAN IN SAID LAST MENTIONED ZONE TO THEREBY ASSURE A BAROMETRIC HEIGHT FOR THE DISCHAGING OF THE CONFINED STREAM OF MOLTEN METAL, WHICH IS LESS THAN THE NORMAL BAROMETRIC HEIGHT THEREOF. 